This invention relates to an improved end for rigid containers. More particularly it relates to an end which has been designed to provide superior buckling resistance from internal pressure.
Buckling is a condition which results when the internal forces within the can exceed the strength of the end thereby causing a portion of the end panel including the countersink wall to bulge upwardly. The resulting bulge may interfere with can stacking, functioning of the easy open features including rupture of the score line, or even cause failure of the double seam. While a possible solution to the buckling problem is to increase the gauge of the end stock, the high volume of production in the container industry makes even a modest increase in material usage undesirable. While considerable effort has been directed to the improvement of end design, if the improvements are to be commercially acceptable they must be compatible with the constraints and standards established by the practitioners of the art. The United States Brewers Association has established standards for Flush Panel and Ring Pull Aluminum Ends which are employed as closures for seamless aluminum cans. These standards, which define the critical dimensions of the ends are listed in Table 1 which is taken from the USBA specification dated 9-1-77. FIG. 7, also taken from the USBA specification, defines the location of these dimensions on the end.
Three dimensions in Table 1 are of particular interest, item B the countersink diameter, item E the countersink radius and item F the countersink depth. These dimensions ensure that the seaming chuck will properly enter the countersink area and engage the end to effect end rotation during seaming.
Two additional dimensions item G panel height and item H panel radius are also of interest although it should be noted that these items have been deleted from the most recent USBA standards.
TABLE I __________________________________________________________________________ (Refer to FIG. 7) USBA DIMENSIONS FLUSH PANEL AND RING PULL ALUMINUM ENDS SEAMLESS ALUMINUM CANS Dimension Key 206 Diameter 207.5 Diameter 209 Diameter 211 Diameter __________________________________________________________________________ A. Curl Diameter 2.614 .+-. .010 2.730 .+-. .010 2.840 .+-. .010 2.945 .+-. .010 B. Countersink Diameter 2.150 Ref. 2.256 Ref. 2.356 Ref. 2.475 Ref. (Die Dimension) C. Curl Height-Ends/2 Inches 21 .+-. 2 21 .+-. 2 21 .+-. 2 21 .+-. 2 Individual End Measurement 0.090/0.105 0.090/0.105 0.090/0.105 0.090/0.105 D. Curl Opening .121 Min. .121 Min. .121 Min. .121 Min. E. Countersink Radius .030 .+-. .005 .030 .+-. .005 .030 .+-. .005 .030 .+-. .005 F. Countersink Depth .250 .+-. .005 .252 .+-. .005 .253 .+-. .005 .253 .+-. .005 G. Panel Height.sup.(2) .066 .+-. .004 .066 .+-. .004 .066 .+-. .004 .066 .+-. .004 H. Panel Radius.sup.(3) .030 .+-. .005 .030 .+-. .005 .030 .+-. .005 .030 .+-. .005 __________________________________________________________________________ .sup.(1) United States Brewers Association September 1, 1977 .sup.(2) In the standards dated 227-81 this dimension is limited to a tolerance. .sup.(3) In the standards dated 227-81 this dimension has been deleted.
A recent patent, U.S. Pat. No. 4,031,837 discloses a method for reforming ends to improve buckle resistance. A basic end is reformed to decrease the radius of curvature of the countersink groove from the standard 0.030" to 0.020" with a 0.024" increase in groove depth. The reforming process reportedly increased buckle resistance from 89 PSI to 105 PSI.
Also of interest is U.S. Pat. No. 3,843,014 which discloses a deep countersink groove with a radius of curvature which varies between 0.020" and 0.047" and where the included angle between the walls of the countersink groove may vary between 7.degree. and 34.degree. with relatively little loss of buckle resistance. The depth of the countersink groove is substantially greater than the limits set by USBA so that such an end is incompatible with the existing equipment.
U.S. Pat. No. 3,774,801 relates to a buckle resistant can end which is formed with a diagonal sloping inner wall re-enforced with at least two peripheral radially separated concave areas of curvature. The end is predomed but no details regarding conformance to USBA standards are disclosed in the patent.
Finally, U.S. Pat. No. 3,441,170 is also of interest in that it discloses a method to control rather than resist buckling. The panel radius, which joins the central panel wall with the inner wall of the countersink groove is coined. The coining increases the excess metal available for bulging and also reportedly enables the radius to act as a hinge so that the buckling occurs but in a controlled manner.
It is an object of this invention to provide a can end which is strengthened to resist buckling but which is compatible with the industry standards.
Another object of this invention is to provide an end which is sufficiently strengthened to permit a reduction in the gage of the end stock.
A further object of this invention is to provide an improved end which will permit higher pasteurization temperatures thereby enabling production lines to operate at higher speeds.
Finally, it is an object of this invention to provide an improved can end which may be readily manufactured with only minor changes in existing equipment.